Digital still cameras and digital video cameras that have become increasingly popular in recent years convert an image signal, which is the result of sensing an image by an image sensing device such as a CCD sensor, to image data in a digital format and store this image data on a recording medium such as a memory card.
Such digital image data can readily be corrected, manipulated and printed by a computer and has come to be utilized in the ordinary home. At the same time, owing to the spread of networks, particularly the Internet, it is now easy for digital image data to be circulated among an unspecified number of users.
Against this background, the necessity for imaging apparatus such as digital still cameras and digital video cameras has grown explosively.
The widespread use of personal computers and the like has made the copying of digital data easier and less expensive. In addition, easier access to the Internet has facilitated and lowered the cost of distributing digital data. As a consequence, even ordinary individuals can now create and distribute copies of digital images easily and inexpensively for purposes beyond private use. Accordingly, though the handling of digital images does not pose a major problem so long as it involves photography for personal enjoyment, the fact that such image data can be copied and distributed easily by unauthorized individuals has not gone unnoticed by those who circulate digital images as a business.
Thus, a problem which arises is that protection of the copyright of photographers, etc., is not satisfactory. Means for protecting copyright is strongly desired for digital image data obtained by photography.
A technique referred to as an “electronic watermark” has undergone extensive research for the purpose of realizing copyright protection of digital image data. This technique is one in which a portion of the data in digital image data or digital audio data is embedded with separate information by superposition in such a manner that the information is rendered insensible or intentionally sensible to a human being, depending upon the particular purpose. When necessary, only a user having the right or qualifications can extract or remove the embedded separate information.
In regard to the principle of electronic watermarking, reference will be had to the specifications of Japanese Patent Application Laid-Open Nos. 10-290359 and 10-150517 to describe, in accordance with FIGS. 9A and 9B, a case where digital information is image information and, moreover, the embedded information is not sensible (or is very nearly insensible) by the user.
FIG. 9A is a diagram illustrating the flow of processing for embedding separate information (embedded data) in image information.
First, an original image (digital image data 401 illustrated in FIG. 10) is divided into a plurality of blocks each of which (block 402 in FIG. 10) is composed of n×m pixels (partitioning processing 901). Next, an orthogonal transform such as a discrete cosine transform (DCT) is applied to each block obtained by division, thereby obtaining an n×m matrix of frequency components (orthogonal transform processing 902).
Before embedding data, an embed component, which indicates in which component of the frequency-component matrix obtained by the orthogonal transform processing the data is to be embedded, is decided based upon a random number, an amount of alteration indicating the extent to which the value of this frequency component will be altered is decided, then the embed component and the amount of alteration are acquired and stored as key information.
By selecting, e.g., a low-frequency portion of the frequency-component matrix as the embed component, the data can be embedded so as not to be sensible by a human being. Further, by changing the amount of alteration, the difference relative to the original value of the frequency-component matrix can be changed. This makes it possible to control the decline in image quality.
The value of the frequency-component matrix of each selected block is changed based upon the embed component and amount of alteration serving as key information 907, thereby embedding embed data 906 (embed processing 903). Furthermore, the frequency-component matrix of each block in which the embed data has been embedded is subjected to an inverse orthogonal transform to obtain an image of a plurality of blocks of n×m pixels each (inverse orthogonal transform processing 904).
Finally, images of the plurality of blocks obtained by the inverse orthogonal transform are connected to obtain a watermark image in which embed data has been embedded (reconstruct processing 905).
FIG. 9B is a diagram illustrating the flow of processing in a case where embed data is extracted from the watermark image. First, the watermark image is divided into a plurality of blocks each of which is composed of n×m pixels (partitioning processing 911). Next, an orthogonal transform such as a discrete cosine transform (DCT) is applied to each block obtained by division, thereby obtaining an n×m matrix of frequency components (orthogonal transform processing 912). Furthermore, the embed component and amount of alteration are obtained from key information 914 that was used at the time of embedding, thereby extracting the embed data from the frequency-component matrix of each block (extraction processing 913).
The watermarking technique according to the above description is advantageous in that (1) the embedded data cannot be extracted without the key information used at the time of embedding; (2) since the embed component in the key information is created based upon a random number, the component is not fixed, thereby making it difficult to decode the embedded data; (3) by specially adapting the embed component, data can be embedded so as not to be sensible by a human being; and (4) the degree to which image quality declines can be controlled by changing the amount of alteration.
An “invisible-data embedding” method through which embedded data is rendered invisible to a human being has been described. As mentioned earlier, however, a “visible-data embedding” method also is available. According to this method, information such as copyright information is embedded in an original image with the intention of being made visible to a human being. This has the effect of causing a third party to abandon the idea of utilizing an image unjustly. For details relating to a visible-data watermarking technique, see the specification of U.S. Pat. No. 5,530,759 (Japanese Patent Application Laid-Open No. 8-241403).
Techniques for authenticating specific individuals are being researched extensively from the standpoint of protecting privacy and providing security.
A number of methods have generally been employed for authenticating individuals. Examples are a method through which only a specific person is verified by a key, card or seal in his or her possession, and a method through which only a specific person is verified by entry of a password or secret code number known only by the person. A fundamental problem with this method is that it is comparatively easy for another person to pose as the specific person by way of theft, counterfeiting or leakage of information, etc.
Accordingly, a method that has become the focus of attention as an alternative to the above method is a biometric personal authentication method that employs a physical characteristic of a specific person to undergo authentication.
It is required that a physical characteristic be unique and person-specific, exhibit randomness and not change over a long period of time. When deployment in an apparatus for performing personal authentication is taken into account, facts to be considered are the time needed to acquire the data needed for authentication and the cost of the apparatus. At the present time, fingerprints, palm prints, iris patterns, voice prints and facial appearance are in wide use as physical characteristics.
Japanese Patent Publication 8-504979 (Japanese translation of PCT International Publication WO94/09446) will be described in general terms with regard to the principle of personal authentication using an iris pattern. FIG. 11 is a flowchart of processing up to a decision as to whether a person being tested is a specific individual or not.
First, the eyeball image of the person is acquired by controlling illumination and focus (1101). When the eyeball image is obtained, the eyelid and eyelash are detected, the pupil-iris boundary 21 and outer boundary 22 of the iris are detected, as shown in FIG. 12, and a coordinate system is set up upon dividing the eyeball into areas 23 referred to as analysis bands (1102).
Next, image analysis (1103), which mainly entails extracting a change in shading of the analysis bands, is performed, and coding is performed based upon the result of analysis (1104). The personal authentication code generated by coding is expressed by a fixed-length array of bits indicated by “1”s and “0”s.
Matching is performed (1105) between the personal authentication code thus coded and a personal authentication code 1107 serving as a template previously acquired from the specific individual. More specifically, the degree of agreement between the two codes is calculated in accordance with a certain evaluation function and, if a fixed threshold value is exceeded, it is decided that the two codes are personal authentication codes sampled from the same individual (1106).
Further, in case of a fingerprint or palm print, the image of the fingerprint or palm print of interest is acquired, the image is coded based upon ridge endings or ridge bifurcations, which are the minutia of the ridges that constitute the fingerprint or palm print, and matching is performed to confirm the individual's identity.
The specification of Japanese Patent Application Laid-Open No. 2000-196998 discloses a method that uses the above-described technique to embed eye information in a photographic image directly as a watermark.
In accordance with this method, an iris pattern or retinal pattern is extracted from an eyeball image acquired at substantially the same time the image of a subject is taken, and the extracted pattern is embedded in the photographic image. As a result, the photographic image and the photographer information are placed in one-to-one correspondence and there is no way for a third party to intervene. This method is effective in that it affords a high reliability as far as copyright information is concerned.
However, the above method necessitates the task of acquiring the eyeball image at approximately the same time that the image of the subject is taken. There are also cases where the method necessitates the additional task of extracting the iris pattern or retinal pattern from the eyeball image and converting this pattern to a personal authentication code by coding means that relies upon image processing. In a digital image sensing device such as a digital still camera, such a task coincides, sequentially speaking, with the timing at which maximum load is imposed upon processing of the subject image at the time of photography. When eyeball-image processing is executed along with subject-image processing, therefore, the overall processing requires a great amount of time. This means that the photographer must wait a while before the next photo can be taken, resulting in possible loss of photographic opportunities.
The imposition of a heavy processing load in this fashion is not limited to a personal authentication method that uses an iris or retinal pattern but is a common problem also in other biometric personal authentication methods that subject personal biological differences to authentication coding by image processing or the like.
When the eyeball image of a photographer is acquired every time an image is taken, the photographer's eye may be closed at the moment of acquisition or an eyelash or strand of hair may interfere. In view of the fact that this can happen frequently, the eyeball image may not always be acquired properly. Furthermore, since the pupil of the photographer's eye opens when an image is taken under low illumination, as is the case indoors, the area of the iris pattern becomes comparatively small and it may not be possible to convert the pattern to an accurate personal authentication code.
Thus, the acquisition of a biological image is affected greatly by the condition of the photographer and surroundings at the time. When the biological image is acquired at the same that an image is taken, an acceptable biological image will not necessarily be obtained. Accordingly, the method of acquiring a biological image at the same time that a subject is photographed is accompanied by considerable disadvantages and risks.